Regarding photoconductive materials used in an electrophotographic photoreceptor, various inorganic and organic photoconductive materials have been known, when the organic photoconductive materials are used for an electrophotography, they have advantages such as film transparency, good film making property, flexibility and good cost-performance. When the organic photoconductive materials are used, a laminate type electrophotographic photoreceptor which is function-separated into a charge generating layer and a charge transporting layer has been proposed in order to improve sensitivity and durability of the photoreceptor.
Recently, the demand for extending the light-sensitive wavelength range of organic photoconductive materials which have heretofore been proposed up to the near infrared wavelength range of semiconductor lasers (780 to 830 nm) so as to use the materials as a photoreceptor for a digital recording system such as a laser printer. From the view point, squalilium compounds (as disclosed, e.g., In JP-A-49-105536 and JP-A-58-21416), triphenylamine trisazo compounds (as disclosed In JP-A-61-151659) and phthalocyanine compounds (as disclosed, e.g., In JP-A-48-34189 and JP-A-57-148745) have been proposed as photoconductive materials for semiconductor lasers.(the term "JP-A" as used herein means an "unexamined published Japanese patent application")
Where organic photoconductive materials are used as light-sensitive materials for semiconductor lasers, they are needed to satisfy the conditions that the light-sensitive wavelength range is extended up to a long wavelength range and that the sensitivity and durability of the photoreceptors to be formed therefrom are good. The above-mentioned organic photoconductive materials do not sufficiently meet the conditions.
In order to overcome these drawbacks, the abovementioned organic photoconductive materials have been researched and Investigated energetically. In particular, many reports relating to phthalocyanine compounds have heretofore been disclosed.
In general, it Is known that phthalocyanine compounds have various crystal forms, depending upon the difference in the manufacture method and treating method, and that the difference in the crystal form has a great influence on the photoelectric conversion characteristics of phthalocyanine compounds. Regarding crystal forms of phthalocyanine compounds, for example, with respect to copper phthalocyanine, various crystal forms of .alpha., .epsilon., .pi., x, .rho., .gamma. and .delta. are known in addition to a stable crystal form of .beta.. It is also known That these crystal forms are mutually transferable to each other by mechanical strain force, sulfuric acid treatment, organic solvent treatment or heat treatment, (as described, e.g., in U.S. Pat. Nos. 2,770,629, 3,160,635, 3,708,292 and 3,357,989). Regarding metal-free phthalocyanine, crystal forms such as .alpha., .beta., .gamma., .tau. and x are Known and the x type phthalocyanine is described In JP-B-44-14106, JP-B-49-4338 and JP-A-4-227768. (the term "JP-B" as used herein means an "examined published Japanese patent application") In these specifications, it is disclosed that the x crystal form of phthalocyanine has a good electrophotographic characteristics compared to another crystal form of metal-free phthalocyanine and is good in the dispersibility in a binder resin. However, the x type phthalocyanine is still insufficient in the point of sensitivity.
On the other hand, some novel crystal forms of high sensitive gallium phthalocyanine halide have been proposed in JP-A-5-98181.
However, the above gallium phthalocyanine halide crystals are not always sufficient in the dispersibility in binder resins and have problems on the stability of the dispersion and they often cause drawbacks of fog or black spots in images formed. Thus, a further improvement has been desired.
On the other hand, as a general improving method of the dispersibility of pigments, there exist modifications of pigment surface by additives such as silane coupling agent or titanate coupling agent or pigment surface treatment by plasma CVD. The former causes decrease of sensitivity and increase of the residual potential, and the latter makes the process complicated and increases the manufacturing cost and thus these methods have no practical use.
The present invention has been made in view of the above-mentioned situation.